Rāhui over Waitematā Harbour lifted
Ngāti Whātua Ōrākei – the tangata whenua and ahi kā of central Tāmaki Makaurau – has formally lifted the rāhui over the Waitematā Harbour. The rāhui was put in place by Ngāti Whātua Ōrākei on September 28 in response to the high-volume wastewater overflows caused by the sinkhole that blocked the Ōrākei main sewer. Ngāti Whātua Ōrākei Trust chair Marama Royal says, "After close consultation with Watercare, and having conducted our own assessments, we are now confident that the mauri of our cherished Waitematā has recovered sufficiently,” she says.
The Safeswim website continues to be the best source of up-to-date information about water quality and other potential hazards at beaches in Tāmaki Makaurau.
Design of the permanent repair is progressing well
Finalising design of the structural liner and rehabilitation works has been the key focus recently.We have ordered the pre-fabricated glass-reinforced plastic liner for the repair of the broken section of pipe in the Ōrākei main sewer. It will be manufactured overseas and flown into the country before Christmas. We plan to start work on the repair early in the new year.
Please only flush the 3Ps
It’s more important than ever to only flush the 3Ps – pee, poo and toilet paper. This is because the temporary bypass pumps are more susceptible to blockages from things like wet wipes and other rubbish that shouldn’t be flushed down the loo.
Wastewater bypass solution continues to operate successfully
It was a massive 20-day effort to get it planned and built in record time, but the the wastewater bypass solution is continuing to operate successfully. Our crews began work on the bypass on Thursday 28 September after a sinkhole formed above the Ōrākei Main Sewer and the pipe was blocked when the land caved in. The bypass has significantly reduced overflows into the Waitematā Harbour. The temporary pump station (see below) can handle flows up to 600 litres per second.
The 400-500 metres of bypass pipes run overground through Alberon Reserve.
We currently have an extensive environmental monitoring programme underway, which includes routine water quality sampling at multiple locations in the Waitematā Harbour along with regular oyster sampling to check for any accumulations of heavy metals or bacteria. The harbour environmental testing programme will cease on 22 December and return to business as usual.
Use of oysters
We have placed bags of oysters at various locations. Samples from these bags will be tested every fortnight for bacteria and heavy metals. This information will supplement our data from the water sampling programme.
Routine beach inspections
So far there has not been any noticeable wastewater debris on beaches.
Sea Cleaners Trust carrying out routine inspections of the harbour
So far they haven’t seen any more debris in the harbour than they normally would.
Inspecting the sea bed
We’re also planning to inspect the sea bed using underwater cameras, when weather and harbour conditions allow.
On the afternoon of Monday 25 September, we were alerted to a hole in the ground by a company undertaking work at a site on St Georges Bay Rd, above the Ōrākei Main Sewer. This 2.1m-diameter brick sewer, approximately 13 metres underground, serves large parts of central and west Auckland. The top of the wastewater pipe had collapsed and the sewer had become completely blocked.
The diagram below shows the impact of the sinkhole on the Ōrākei main sewer. Our crews have been working around the clock using hydro-excavation (jetting water) and a vacuum sucker truck to remove debris from the blockage inside the sewer. Crews sprayed a concrete like product on the slope to prevent more material falling in.
Concrete-spraying on the slope of the sinkhole was carried out to prevent further debris falling into the hole. Scaffolding has been erected to provide our team with safe access to the sewer in preparation for repairs.